How to merge two video without audio stream in ffmpeg

Solution 1:

Simply, you don't have an audio stream in your image videos created. There you have only a video stream. So when you try to get an audio stream from a source where an audio stream is not available you get this error. In yous first command you just create a video out of set of images and there is no audio involved. So in the output of that command will have only a video stream. In your second command [0:0] refers to the first stream of the first input and it is the video stream in your case. [0:1] refers to the second stream of the second input and where it dies not exists.

As you don't have an audio with any of the videos you are concatenating simple fix would be as follows.

ffmpeg -y -i video1.mp4 -i video2.mp4 -filter_complex 
"[0:0][1:0]concat=n=2:v=1:a=0" output.mp4